In recent years, a CRT display as an image display device has been gradually replaced by a flat panel display (FPD), which is lighter and thinner than the CRT display, such as a liquid crystal display (LCD), a plasma display (PDP), or an organic light-emitting diode (OLED) display. Further lightening of any such FPD is being promoted, and hence there arises a need for further thinning a glass substrate corresponding to one of the main components of the FPD.
Further, for example, there is a growing use of an organic light-emitting diode not only for applications to a display that uses TFTs to blink light of three primary colors, but also as a plane light source, such as a backlight of the LCD and a light source for interior illumination, which emits only monochrome (for example, white) light. An illumination device that uses the organic light-emitting diode as alight source may have a freely deformable light-emitting surface as long as the organic light-emitting diode is constructed of a flexible glass substrate. Therefore, from the viewpoint of ensuring sufficient flexibility, there is also promoted further thinning of the glass substrate to be used for this type of illumination device.
Therefore, as described in, for example, Patent Literature 1 below, there has been developed a film-like thin glass sheet (glass film) having a thickness of several hundreds of micrometers or less. In general, as described also in Patent Literature 1, this type of glass film is successively formed by a forming device that employs a so-called downdraw method. For example, a delivery direction of the elongated glass film thus successively formed is converted from a vertical direction to a horizontal direction, and then, during a period in which a horizontal conveyance section of a conveyance device continuously delivers the glass film to a downstream side, both widthwise end portions of the glass film are cleaved as necessary. Then, the glass film is introduced into a cutting step for obtaining a thin glass sheet having a predetermined dimension, or a rolling step for obtaining a glass roll.
Note that, the glass roll has an advantage of higher workability in packaging and shipping as compared to the thin glass sheet cut into a predetermined dimension. Further, in the case of the glass roll, a so-called roll-to-roll system can be employed so that cleaning, drying, and antistatic processes can be performed successively for the glass film (see FIGS. 12 and 13 of Patent Literature 1), and further a functional film can be formed successively on an effective surface of the glass film in a subsequent step or at a panel manufacturer (see Patent Literature 2 below). Thus, the glass roll also has an advantage in that various kinds of processes can be executed efficiently for the glass film. As described above, the glass roll has many advantages, and therefore a demand therefor is rapidly increasing.
By the way, when the glass film is sequentially rolled into a roll shape under a state in which a tensile force is not sufficiently imparted to the glass film, portions of the rolled glass film cannot be brought into close contact with each other, and so-called weaving is likely to occur due to an effect of, for example, vibrations to be applied during transportation. When the weaving has occurred, in a case where the glass film is unrolled from the glass roll and a predetermined process (processing) is executed for the unrolled glass film, the unrolled glass film is displaced in an axial direction of a roll core. Therefore, when such a glass roll is introduced into various processing devices in the roll-to-roll system, distortion is accumulated in the unrolled glass film because various members constituting the processing devices are positionally fixed. Such accumulation of the distortion may increase a risk of damage to the glass film. Thus, when obtaining the glass roll, it is desired that the glass film be rolled under a state in which an appropriate tensile force is imparted to the glass film so as to prevent the weaving.
As a specific method for rolling an elongated film-like workpiece while imparting an appropriate tensile force to the workpiece, methods described in Patent Literatures 3 and 4 below may be taken as examples. In the method described in Patent Literature 3, while a roll for unrolling a glass film and a roll for rolling a glass film are rotationally driven in opposite directions, and in this state, nip rolls interposed between the roll for unrolling a glass film and the roll for rolling a glass film impart a delivery force toward the roll for rolling a glass film from the roll for unrolling a glass film to the film-like workpiece unrolled. That is, in this method, rotational speed, torque, and the like of each of the roll for unrolling a glass film, the roll for rolling a glass film, and the nip rolls are set (managed) appropriately so that an appropriate tensile force is imparted to the film-like workpiece, and in this state, the rolling and unrolling of the film-like workpiece are progressed. In the method described in Patent Literature 4, suction rolls are interposed between the roll for unrolling a glass film and the roll for rolling a glass film. Each suction roll has innumerable holes in its outer peripheral surface, and is capable of sucking the film-like workpiece toward the outer peripheral surface by setting an interior of the suction roll to a negative pressure state.